Synthesis of CO2-one adsorbent for CO2 removal

ABSTRACT

A new adsorbent CO 2 -ONE for removal of acidic gases such as carbon dioxide and hydrogen sulfide was developed from hydrothermal reaction of natural limestone with natural kaolin via sodium hydroxide. Several synthesis conditions were employed such as initial concentration of NaOH, weight ratio of limestone to kaolin, reaction temperature and pressure. The produced Ca—Na—SiO2-Al2O3 samples were characterized using XRD and EDS and showed that a mixture of Gehlenite Ca 2 Al(Al 1.22 Si 0.78 O 6.78 )OH 0.22  and Stilbite Na 5.76 Ca 4.96 (Al 15.68 Si 56.32 O 144 ) with percentage of 43 and 57 was successfully produced, respectively. Another produced sample showed the presence of Gehlenite Ca 2 Al(Al 1.22 Si 0.78 O 6.78 )OH 0.22 , Stilbite Na 5.76 Ca 4.96 (Al 15.68 Si 56.32 O 144 ) and Lawsonite CaAl 2 Si 2 O 7 OH 2 (H 2 O) with percentage of 4.1 and 7.4 and 88, respectively.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to aCa—Na—SiO₂—Al₂O₃/Sodium-Calcium-Aluminosilicate composition, a method ofmaking Ca—Na—SiO₂—Al₂O₃/Sodium-Calcium-Aluminosilicate composition, anda method for using the Ca—Na—SiO₂—Al₂O₃/Sodium-Calcium-Aluminosilicateas an adsorbent for the removal of CO₂ from a gaseous composition.

2. Description of the Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

Environmental pollution is one of the major problems facing humanitythis century. Emission of toxic gases into the atmosphere is a primarysource of air pollution. Combustion of heavy oil, coal and oil shale,exhausts from automobiles, as well as smelting operation, sulfuric acidmanufacturing and metallurgical processes are the main sources fordischarging of these toxicants into the atmosphere. These gases include:sulfur oxides (SO_(x)), nitrogen oxides (NO_(x)), carbon oxides (CO_(x))and hydrogen sulfide (H₂S). Once these gases enter the troposphere, someof them react with water and oxygen molecules to form acid rain andreturn back to the ground. Other gases such as carbon dioxide andfluorinated hydrocarbons can escape to the outer layer of the atmosphereleading to depletion of the ozone layer and affect global warming.

Carbon dioxide specifically reached an alarming level in the atmospherewhere a major change in global climate was noticed since the beginningof the 21^(st) century. It is estimated that the net increase of 13,000million tons of CO₂ is added to the atmosphere annually¹. The risinglevel of CO₂ is already affecting the atmosphere, sea level andecological systems. The global sea level has raised 10 to 20 cm over thepast century. In this current century this level is expected to rise by88 cm. The current atmospheric concentration of carbon dioxide is 391.8ppm, which is 30% greater than that of the pre-industrial level.

Natural gas accounts for emission of large quantity of CO₂. In 2004 theglobal emission of CO₂ from natural gas was 5.3 billion tons, while coaland oil produced 10.6 and 10.2 billion, respectively. This value isexpected to increase to 11 billion tons which exceeds the one fromcombustion of coal and oil².

Adsorption is a promising technology for capturing of CO₂ from exhaustgas downstream. The advantage of this process is to utilize low costadsorbents, naturally occurring materials or by-products of chemicalindustries that have high removal capacity. Among these materials areactivated carbons, zeolites, fly ash, limestone and different metaloxides⁶⁻¹².

Limestone and kaolin are natural abundant materials which have largereserves worldwide. The main uses of these materials are in the cementindustry and in the architectural industry.

Adsorption of carbon dioxide can be attained by different types ofadsorbents. Generally those adsorbents can be classified into threedifferent groups; organic-based materials, inorganic solids containingsome transition metals, or activated carbonaceous materials. Severalresearch articles were published in this regard. A summary of the mostrecent and promising results is provided below:

Sevilla and Fuertes¹⁴ utilized activated carbon material prepared foradsorption of CO₂ from a CO₂—N₂ gas mixture. The adsorbent showed asurface area of 1020 m²/g and a pore volume of 0.91 cm³/g which can beenhanced to 2660 m²/g and 1.38 cm³/g, respectively, by treatment withpotassium hydroxide at 600-800° C. The sorption capacity was 3.2 mmolCO₂/g at 25° C.

Cen et al.¹⁵ used commercial activated carbon adsorption of CO₂ fromeffluent of combustion process. A breakthrough adsorption experiment wasperformed with simulated flue gas of 12 vol. % CO₂. The kineticparameters that affect the rate of adsorption of CO₂ in a fixed bedcolumn was evaluated.

Schell et al.¹⁶ studied adsorption equilibrium of CO₂, H₂ and N₂ onAP3-60 commercial activated carbon using a Rubotherm Magnetic SuspensionBalance and gravimetric-chromatographic method. The results were fittedto Langmuir and Sips isotherms and compared to binary measurements.

Shao et al.¹⁷ tested several carbonaceous mesoporous materials foradsorption of CO₂ by gravimetric analyzer (IGA-003, Hiden). It was foundthat CO₂ adsorption capacity of 909 mg/g has been achieved by the typeACB-5 at 298 K and 18 bar.

Karadas et at.¹⁸ prepared metal carbonates consisting of Zn2+, Mg2+, andCu2+ and measured the adsorption of CO₂ by this material usingthermogravimetric analysis (TGA).

Abid et al.¹⁹ prepared zirconium-metal organic frameworks (Zr-MOFs) foradsorption of CO₂ and CH₄. The removal capacities for both gases were8.1 and 3.6 mmol/g, respectively, obtained at 273K, 988 kPa. Addition ofammonium hydroxide during the synthesis of MOF lowered the sorptioncapacities but enhanced the selectivity of CO₂ over CH₄.

Wang et al.²⁰ investigated the ability of Si-doped lithium zirconatesorbents for adsorption of CO₂. Doping silicon in the adsorbent matrixcould improve the sorption capacity.

Modak et al.²¹ synthesized iron containing porous organic polymers(Fe-POPs). The adsorbent possessed a high BET surface area andappreciable CO₂ capture of 19 wt % at 273 K and 1 bar.

Kauffman et al.²² evaluated the selectivity of adsorption of CO₂ fromN₂, CH₄, and N₂O gas mixture by dynamic porous coordination polymerusing ATR-FTIR spectroscopy, GC, etc. They proved that all the selectedtechniques indicate high selective adsorption of CO₂ from CO₂/CH₄ andCO₂/N₂ mixtures at 30° C., while the system CO₂/N₂O is not selective.

Wang and Yang²³ enhanced the porosity of silica SBA-15 by two templateremoval methods followed by amine grafting and used for removal of CO₂from CO₂/N₂ gas mixture. The CO₂ sorption capacity was increased from1.05 to 1.6 mmol/g when the silanol density was increased from 3.4 to8.5 OH/nm² and the grafted amine loading was increased from 2.2 to 3.2mmol/g.

Zhao²⁴ investigated the adsorption of CO₂ by Mg-modified silica. Theydeveloped the Mg-zeolite by methods of co-condensation, dispersion andion-exchange where Mg²⁺ ions were introduced into SBA-15 and MCM-41, andtransformed into MgO in the calcination process. The adsorption capacityincreased from 0.42 mmol/g of pure silica SBA-15 to 1.35 mmol/g ofMg—Al-SBA-15-I1 and increased from 0.67 mmol/g of pure silica MCM-41 to1.32 mmol/g of Mg-EDA-MCM-41-D10 by ion exchange and dispersion methods,respectively.

Sonawane and Nagare²⁵ investigated theoretically the reactivity ofSi-doped single walled carbon nanotubes for O₂, CO₂, SO₂ and NO₂ usingdensity functional theory. They showed that the charge density, bindingenergy and density and charge transfer of state are the main factors forchemical adsorption of these gases by Si-CNT.

Xue et al.²⁶ showed that the selectivity and adsorption capacity of CO₂were increased by addition of piperazine to methyldiethylamine duringthe modification of the surface of silica gels. The exit concentrationfrom a column packed with this adsorbent has decreased from 13 wt. % toless than 0.05 wt. %.

Li²⁷ investigated the adsorption dynamics of CO₂ by a bed of sodiumoxide promoted alumina. The breakthrough curve model was developed basedon the experimental data.

Zukal et al.²⁸ measured the adsorption isotherm of CO₂ on the Na-Azeolite in the temperature range from 273 to 333 K. The data were fittedto a periodic density functional model improved for the properdescription of dispersion interactions.

Reinik et al.²⁹ synthesized calcium-silica-aluminum hydrate from oilshale fly ash by reaction with 5M sodium hydroxide at 130° C. Thematerial was tested for its adsorption capacity of CO₂ usingthermo-gravimetric analysis. The results showed an increase in capacityfrom 0.06 mass % when using untreated ash to 3-4 mass % after alkalinehydrothermal activation with NaOH.

The present disclosure describes mixtures of aluminosilicates linkedwith calcium and sodium oxides in a crystalline structure. The materialswere used for adsorption of acidic gases such as CO₂ from a gas stream.

BRIEF SUMMARY OF THE INVENTION

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

One embodiment of the present invention a includes a compositionCa—Na—SiO₂—Al₂O₃/Sodium-Calcium-Aluminosilicate composition.

In another embodiment theCa—Na—SiO₂—Al₂O₃/Sodium-Calcium-Aluminosilicate is used as an adsorbent.

In another embodiment the Ca—Na—SiO₂—Al₂O₃ includes a mixture ofGehlenite and Stilbite.

In another embodiment the Ca—Na—SiO₂—Al₂O₃ includes a mixture ofGehlenite, Stilbite and Lawsonite.

In another embodiment the synthesis of Ca—Na—SiO₂—Al₂O₃ includes mixinglimestone and kaolin with a base to form a mixture, hydrothermallytreating the mixture with nitrogen, and calcining the mixture to form amixture including Gehlenite and Stilbite.

In another embodiment a method includes adsorbing CO₂ from a gaseouscomposition by contacting the gaseous substance with theCa—Na—SiO₂—Al₂O₃/Sodium-Calcium-Aluminosilicate in an isothermal column.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is an X-Ray diffraction diagram for the CO₂-ONE adsorbent;

FIG. 2 is an X-Ray diffraction diagram of natural limestone, calcite,and quartz;

FIG. 3 is an X-Ray diffraction diagram of natural kaolin, kaolinite, andanatase;

FIG. 4 is a diagram of a breakeven curve for adsorption/desorption ofCO₂ by CO₂-ONE adsorbent;

FIG. 5 is a diagram of a breakeven curve for adsorption/desorption ofCO₂ by limestone;

FIG. 6 is a diagram of a breakeven curve for adsorption/desorption ofCO₂ by kaolin;

FIG. 7 is a diagram of the effect of temperature on the adsorption ofthe CO₂-ONE adsorbent; and

FIG. 8 is a diagram of the effect of the regeneration cycles on theamount of CO₂ adsorbed, desorbed and reacted onto the CO₂-ONE adsorbent.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views.

A new mixture of aluminosilicates linked with calcium and sodium oxidesin their crystalline structure is disclosed. The produced materials weretested for adsorption of acidic gases such as CO₂ from a gas stream.

The present disclosure relates to aCa—Na—SiO₂—Al₂O₃/Sodium-Calcium-Aluminosilicate composition (e.g., aCO₂-ONE adsorbent) and a method for making the CO₂-ONE adsorbent. TheCO₂-ONE composition is a Ca—Na—SiO₂—Al₂O₃/sodium-calcium-aluminosilicatecomposition. In embodiments of the disclosure the CO₂-ONE compositionmay comprise a mixture of materials such as Gehlenite (e.g.,Ca₂Al(Al_(1.22)Si_(0.78)O_(6.78))OH_(0.22)) and Stilbite (e.g.,Na_(5.76)Ca_(4.96)(Al_(15.68)Si_(56.32)O₁₄₄)). The CO₂-ONE compositionmay contain different amounts of Gehlenite and Stilbite. For example,the Gehlenite may be present in an amount of from 40 to 60% by mass andthe Stilbite may be present in an amount of 40-60% by mass based on thetotal weight of the Gehlenite and Stilbite. Preferably the Gehlenite ispresent in an amount of 41-55, 42-50, 43-48 or 44-46% by mass.Preferably the Stilbite is present in an amount of 45-59, 50-58, 48-57or 50-53% by mass. The CO2-ONE preferably contains at least 50% by mass,more preferably 60%, 70%, 80%, 90%, 95% or 99% by mass of a total amountof Gehlenite and Stilbite, wherein % by mass is based on the totalweight of the CO₂-ONE composition.

In another embodiment the CO₂-ONE composition comprises a mixture ofGehlenite, Stilbite and Lawsonite (e.g., CaAl₂Si₂O₇OH₂(H₂O)). TheGehlenite is preferably present in an amount of 1-10% by mass, morepreferably 2-8, 3-6 or 4-5% by mass based on the total mass ofGehlenite, Stilbite and Lawsonite. The Stilbite is preferably present inan amount of 5-15% by mass, more preferably 6-14, 7-13, 8-12 or 9-11% bymass. The Lawsonite is preferably present in an amount of 80-95% bymass, more preferably 81-94%, 82-93%, 83-92%, 84-91%, 85-90%, 86-89% or87-88% by mass. As is the case for the CO₂-ONE composition thatcomprises Gehlenite and Stilbite without Lawsonite, theLawsonite-containing CO₂-ONE composition preferably contains Gehlenite,Stilbite and Lawsonite in an amount of at least 50% by mass, morepreferably 60%, 70%, 80%, 90%, 95% or 99% by mass based on the totalmass of the CO₂-ONE composition. The CO₂-ONE composition may containother tectosilicate minerals and/or zeolites. Stilbite-Na is preferredover Stilbite-Ca. Because silicon and aluminum ions in Stilbite occupyequivalent positions it is possible for the Si/Al ratio to vary.Variance in the Si/Al ratio must be compensated by adjusting thecorresponding sodium/calcium ratio. The Stilbite is ordinarily presentin the monoclinic 2/m phase although orthorhombic or triclinic phasesmay also be present in minor amounts.

Sorosilicates other than Gehlenite may also be present in the CO₂-ONEcomposition. In some embodiments the Gehlenite may be present in analuminum-rich phase. The Gehlenite has a tetragonal crystal system andmay be interlinked with a crystal system of the aluminosilicateframework structure.

Lawsonite, like Gehlenite, is a sorosilicate mineral but is present inits hydrous calcium aluminum form in the present disclosure. Lawsoniteis preferably present in a major amount in its orthorhombic phase butmay also be present in a minor amount in one or more other phases.

Lawsonite may have an idealized composition of formula ofCaAl₂Si₂O₇(OH)₂. Gehlenite has an idealized formula of Ca₂Al(AlSiO₇).Stilbite has an idealized formula of NaCa₄(Si₂₇Al₉)O₇₂.28(H₂O).

The CO₂-ONE composition may be obtained by treating mixtures of mineralsby heating and/or calcination. Kaolin is a convenient clay mineral thatmay be used as one precursor to the CO₂-ONE composition. Kaolin has anidealized chemical composition of Al₂Si₂O₅(OH)₄ although variations inchemical composition are included. Heating kaolin leads todehydroxylation and formation of materials having a generalized formulaof Al₂Si₂O₇ which may be further heated to separate portions of SiO₂ andform spinels such as Si₃Al₄O₁₂. Calcination of kaolin or a spinel ormetakaolin derived from kaolin can further drive out SiO₂ to formcompounds of general formula Si₂Al₆O₁₅.

The kaolin may be treated in combination with limestone (CaCO₃). Heatingmixtures of kaolin and limestone provides a method of forming theCO₂-ONE composition of the present disclosure. Treating limestone andkaolin with a base such as NaOH under certain temperature andenvironmental conditions forms the CO₂-ONE composition of the presentdisclosure.

First, rocks of limestone and kaolin are crushed. Once the rocks arecrushed, they are sieved into different particle sizes. The particlesizes of the rocks are in the range of 4 mm-650 μm, 3 mm-550 μm, or 2mm-450 μm. Preferably, the particle sizes of the rocks are in the rangeof 2 mm-450 μm. The rocks are then placed in a closed-capped containerfor further use. Limestone and kaolin are mixed using different amountsof a base containing a single —OH functional group. The base can includebut is not limited to sodium hydroxide (NaOH), lithium hydroxide (LiOH),or potassium hydroxide (KOH). Preferably the base is NaOH. The amount ofbase that is mixed with the sample of limestone and kaolin includesdifferent concentrations in the range of including but not limited to 2g/100 mL-40 g/100 mL, 3 g/100 mL-38 g/100 mL, or 4 g/100 mL-36 g/100 mLfor a time period in the range of 30 minutes-2 hours, 45 minutes-2.5hours, or 55 minutes-1.5 hours. Preferably, the amount of base mixedwith the sample of limestone and kaolin includes a concentration in therange of 4 g/100 mL-36 g/100 mL over a time period of 1 hour.

The mixed sample of limestone, kaolin, and base is then placed in ahydrothermal reactor operating at different reaction temperatures in therange of 30° C.-300° C., 40° C.-250° C., or 50° C.-200° C. and apressure in the range of 2 bar-20 bar, 3 bar-18 bar, or 4 bar-15 bar.Preferably, the reaction temperature in the reactor is in the range of50° C.-200° C. and the reaction pressure in the reactor is in the rangeof 4 bar-15 bar. Nitrogen is then introduced to the reactor to maintainthe desired temperature and pressure ranges.

Once the reaction occurs, the produced samples are cooled to roomtemperature. Cooling occurs through a natural process in which thesamples settle and over time the temperature reaches equilibrium withthe air surrounding it. Cooling occurs over a time period in the rangeof 1 hour-3 hours, 1.5 hours-2.5 hours, or 1.75 hours-2.25 hours.Preferably, cooling occurs over a time period of 2 hours.

Following cooling, the dried residue is subject to calcinationtreatment. Calcination can be carried out in shaft furnaces, rotarykilns, multiple hearth furnaces, and/or fluidized bed reactors.Calcination is conducted over a time period of 1-4 hours, 1.25-3.5hours, or 1.5-3.25 hours at a temperature ranging from 400-700° C.,500-650° C., or 525°-575° C. Preferably calcination is conducted forabout 2 hours at a temperature of 550° C. Following calcination, thesample is washed with deionized water, dried and stored to be used in asorption-desorption method. The CO₂-ONE composition is preferably usedas a sorbent for CO₂. By contacting the CO₂-ONE composition withCO₂-containing gaseous phase the CO₂ is absorbed by the CO₂-ONEcomposition and its concentration in the surrounding gaseous environmentis reduced. The CO₂-ONE composition may be used to reduce the amount ofCO₂ in a gaseous environment by an amount of 50-99.5% by mass based onthe total mass of CO₂ present in the gaseous environment. Preferably theCO₂ concentration in the gaseous environment is reduced by an amount of60%, 70%, 80%, 90%, 95% by mass based on the total amount of CO₂ presentin the gaseous atmosphere.

A method of sorption of a sample of CO₂ is carried out by placing afixed amount of different ranges of sample sizes in an isothermalcolumn. CO₂ is introduced to the bed from the bottom of the column usinga fixed flow rate. The initial concentration of CO₂ is in the range of1.6%-2.2%, 1.7%-12.0%, or 1.8%-1.9% and the flow rate of the CO₂ is inthe range of 2 L/min-6 L/min, 3 L/min-5 L/min, or 3.5 L/min-4.5 L/min.Preferably, the initial concentration of CO₂ is 1.87% and the flow rateis 4 L/min. The concentration of CO₂ at the exit stream is measured atdifferent periods of time at one minute intervals ranging from 0minutes-12 minutes. The difference in concentration between the inletand outlet streams is calculated. A similar procedure is carried out todetect the sorption capacity of the sample against CO₂-free gas to useas a comparison.

After having absorbed CO₂ the CO₂-ONE composition may be regeneratedand/or recycled by desorbing the previously-absorbed CO₂. Desorption maybe carried out by heating the CO₂-containing CO₂-ONE composition andpassing one or more inert gases over the CO₂-ONE composition. Atsufficient temperature CO₂ will desorb from the CO₂-ONE composition.Desorption may remove more than 50%, preferably more than 60%, 70%, 80%,90%, 95% of the CO₂ adsorbed thereon from a gaseous environment.

A method of desorption of a sample of N₂ is carried out by placing afixed amount of different ranges of sample sizes in an isothermalcolumn. N₂ is introduced to the bed from the bottom of the column usinga fixed flow rate. The initial concentration of N₂ is in the range of1.6%-2.2%, 1.7%-12.0%, or 1.8%-1.9% and the flow rate of the N₂ is inthe range of 2 L/min-6 L/min, 3 L/min-5 L/min, or 3.5 L/min-4.5 L/min.Preferably, the initial concentration of N₂ is 1.87% and the flow rateis 4 L/min. The concentration of N₂ at the exit stream is measured atdifferent periods of time at one minute intervals ranging from 0minutes-12 minutes. The difference in concentration between the inletand outlet streams is calculated.

Example Preparation of Adsorbent

Rocks of limestone and kaolin were crushed and sieved to differentparticles sizes ranging from 2 mm-450 μm, then placed in a closed-cappedcontainer for further use. A representative sample of each of limestoneand kaolin was mixed with different concentrations of sodium hydroxidefor 1 h then placed in a hydrothermal reactor operated at differentreaction temperature and pressure (Table 1). Nitrogen was introduced tothe reactor to maintain the desired pressure. Upon completion of thereaction, the produced samples were cooled to room temperature andexposed to air for 2 h, then calcinated at 550° C. for 2 h. Then thesample was washed with deionized water, dried and stored inclosed-container for application. Table 1 is presented below.

TABLE 1 Full factorial design for proposed experiments DESIGN EXP RUNCarbonate [NaOH] Temperature Pressure ORDER ORDER (g) A (g/100 ml) B C(bar) D 1 1 2 4 50 15 2 2 6 4 50 4 3 3 6 4 50 15 4 4 2 4 50 4 5 5 2 3650 4 6 6 6 36 50 4 7 7 2 36 50 15 8 8 6 36 50 15 9 9 2 4 200 4 10 10 6 4200 4 11 11 2 4 200 15 12 12 6 4 200 15 13 13 6 36 200 15 14 14 2 36 2004 15 15 6 36 200 4 16 16 2 36 200 15

Example Sorption-Desorption Procedure

Sorption-desorption procedure was carried out by placing fixed amount ofdifferent particle sizes of the produced sample in an isothermal column.Gas stream containing a fixed concentration of CO₂ were introduced tothe bed from the bottom of the column at fixed flow rate. Then theconcentration of CO₂ at the exit stream was measured at differentperiods of time and the difference in concentration between the inletand outlet streams were calculated. Similar procedure was used to detectthe sorption capacity of the sample against CO₂-free gas for comparison.Desorption procedure was similar to the above procedure except thatnitrogen gas was introduced instead of CO2. All the experiments wererepeated at different conditions such as bed temperature and gas flowrate.

A new adsorbent CO₂-ONE for removal of acidic gases such as carbondioxide and hydrogen sulfide was developed from hydrothermal reaction ofnatural limestone with natural kaolin and sodium hydroxide. Severalsynthesis conditions were employed such as initial concentration ofNaOH, weight ratio of limestone to kaolin, reaction temperature andpressure. The produced Ca—Na—SiO2-Al2O3 samples were characterized usingXRD and EDS and showed that a mixture of GehleniteCa₂Al(Al_(1.22)Si_(0.78)O_(6.78))OH_(0.22) and StilbiteNa_(5.76)Ca_(4.96)(Al_(15.68)Si_(56.32)O₁₄₄) with percentage of 43 and57 was successfully produced, respectively. Another produced sampleshowed the presence of GehleniteCa₂Al(Al_(1.22)Si_(0.78)O_(6.78))OH_(0.22), StilbiteNa_(5.76)Ca_(4.96)(Al_(15.68)Si_(56.32)O₁₄₄) and LawsoniteCaAl₂Si₂O₇OH₂(H₂O) with percentage of 4.1 and 7.4 and 88, respectively.

Both produced samples were tested for adsorption/desorption of CO₂ at22° C. and 1 atm, and compared with raw materials and found that for agiven mass of sample of 13.5 g, initial flow rate and concentration ofCO₂ of 4 L/min and 1200 mg/L, respectively, the breakeven adsorptioncurves as follows: for the produced sample it took 59 min to getsaturated with CO₂ while limestone and kaolin took 0.27 and 0.23 min,respectively to reach the same saturating value.

The adsorptions of CO₂ by the treated samples follow chemisorptionsprocess where a chemical reaction between the CO₂ and the surface tookplace. This sorption is enhanced with increasing bed temperature whichconcludes endothermic process at the surface of the produced samples.

The new adsorbent was tested after several regeneration cycles with 14 MNaOH and found that its capacity increases with increasing theregeneration cycles as a result of more Na oxide linked aluminosilicatestructure with the treatment of NaOH. When the initial gas concentrationis 1.87% and the flow rate is 4 L/min, the maximum adsorption capacityinitially is 0.143 mol/g, followed by 0.513 mol/g after 1^(st)regeneration, by 0.435 mol/g after 2^(nd) regeneration, by 0.526 mol/gafter 3^(rd) regeneration, by 1.272 mol/g after 4^(th) regeneration andby 2.223 mol/g after 5^(th) regeneration. FIG. 1 is an XRD for theproduced CO2-ONE adsorbent. FIG. 2 is an XRD of natural limestone,Calcite 34%, and Quartz 66%. FIG. 3 is an XRD of natural kaolin,Kaolinite 83.5% and Anatase 16.5%. FIG. 4 is a graph depicting abreakeven curve for adsorption/desorption of CO2 by CO2-ONE adsorbent.FIG. 5 is a graph depicting a breakeven curve for adsorption/desorptionof CO2 by Limestone. FIG. 6 is a graph depicting a breakeven curve foradsorption/desorption of CO2 by Kaolin. FIG. 7 is a graph depicting theeffect of temperature (5, 15, 25, 35, 50, 60, and 70° C.) on theadsorption of the CO2-ONE adsorbent. The initial CO₂ concentration was18700 mg/L (1.87%). FIG. 8 is a graph depicting the effect ofregeneration cycles on amount of CO2 adsorbed, desorbed and reacted ontoCO2-ONE adsorbent. The initial CO2 concentration was 18700 mg/L (1.87%).

Thus, the foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. As will be understood by thoseskilled in the art, the present invention may be embodied in otherspecific forms without departing from the spirit or essentialcharacteristics thereof. Accordingly, the disclosure of the presentinvention is intended to be illustrative, but not limiting of the scopeof the invention, as well as other claims. The disclosure, including anyreadily discernible variants of the teachings herein, define, in part,the scope of the foregoing claim terminology such that no inventivesubject matter is dedicated to the public.

The invention claimed is:
 1. ACa—Na—SiO₂—Al₂O₃/Sodium-Calcium-Aluminosilicate composition comprising:40-45% gehlenite and 55-60% stilbite.
 2. The composition of claim 1,further comprising one or more acidic gases adsorbed thereon.
 3. Thecomposition of claim 1, comprising 42-44% gehlenite and 56-58% stilbite.4. The composition of claim 1, comprising 43% gehlenite and 57%stilbite.
 5. A method for making the composition of claim 1, comprising:mixing limestone and kaolin with a base to form a first mixture;crystallizing the first mixture using a hydrothermal reactor andnitrogen to form a second mixture; and calcining the second mixture toform a composition comprising gehlenite and stilbite.
 6. The method ofclaim 5 in which the base is NaOH and the base is mixed with limestoneand kaolin in an amount of 4 g/100 mL to 36 g/100 mL.
 7. The method ofclaim 5, further comprising calcining the second mixture at 550° C. for2 hours.
 8. The composition of claim 1, having an acidic gas adsorptioncapacity of 0.10 mol/g-0.2 mol/g after a 1^(st) regeneration cycle. 9.The composition of claim 1, having an acidic gas adsorption capacity of2.0 mol/g-2.5 mol/g after a 5^(th) regeneration cycle.
 10. ACa—Na—SiO₂—Al₂O₃/Sodium-Calcium-Aluminosilicate composition comprising3-6% gehlenite, 5-9% stilbite, and 86-92% lawsonite.
 11. The compositionof claim 10, comprising 4-5% gehlenite, 6-8% stilbite, and 87-91%lawsonite.
 12. The composition of claim 10, comprising 4.1% gehlenite,7.4% stilbite, and 88% lawsonite.
 13. A method for making thecomposition of claim 10, comprising: mixing limestone and kaolin with abase to form a first mixture; crystallizing the first mixture using ahydrothermal reactor and nitrogen to form a second mixture; andcalcining the second mixture to form a composition comprising gehleniteand stilbite.
 14. The method of claim 13, in which the base is NaOH andthe base is mixed with limestone and kaolin in an amount of 4 g/100mL-36 g/100 mL.
 15. The method of claim 13, further comprising calciningthe second mixture at 550° C. for 2 hours.
 16. The composition of claim10, having an acidic gas adsorption capacity of 0.10 mol/g to 0.2 mol/gafter a 1^(st) regeneration cycle.
 17. The composition of claim 10,having an acidic gas adsorption capacity of 2.0 mol/g to 2.5 mol/g aftera 5^(th) regeneration cycle.